1. Field of the Invention
The present invention relates to a method of manufacturing an electrode plate assembly for a lead accumulator and device therefor whereby an electrode plate assembly for a lead accumulator is manufactured by forming, by the cast-on strap method, a strap connecting electrode plates on an electrode plate group constituted by forming a plurality of electrode plates as a stack.
2. Description of the Related Art
As shown in FIG. 11, an electrode plate assembly of a lead accumulator is manufactured by continuously connecting electrode plate leads 6 by means of straps 2a, 2b, by forming respective straps 2a, 2b on the positive electrode plate side and negative electrode plate side on electrode plate leads 6 formed in projecting manner on each electrode plate 3 in an electrode plate group 10 in which there are alternately stacked a plurality of electrode plates 3 of positive and negative electrodes, with interposition of separators 5.
In the case of the electrode plate assembly shown in FIG. 11, an electrode pillar 4 is formed constituting a terminal electrode of an accumulator on a strap 2b and a connector 7 between cells for connecting electrode plate assemblies is adjacently connected to a strap 2a. As shown in FIG. 12, a plurality of thus-formed electrode plate assemblies are accommodated in the electrolyte tank 45 of a lead accumulator, a lead accumulator of the required output voltage being manufactured by effecting connection between straps 2a, 2b of the various electrode plate assemblies. The shape of these straps 2 (2a, 2b) is different depending on the type of lead accumulator and/or the position of their arrangement on the lead accumulator, so in the following description they will be referred to generally as straps 2, irrespective of changes in shape and/or positive/negative polarity. Also, for definiteness in the description given below, the condition in which a plurality of electrode plates 3 are stacked will be called an electrode plate group 10, while the condition in which straps 2 are formed on such an electrode group 10 will be called an electrode plate assembly 1.
FIG. 13 shows the construction of a prior art example of a device for forming a strap 2 on electrode plate group 10 by the cast-on method referred to above. Heaters 42 and cooling-water pipes 41 are provided, the construction being such that heating by means of heaters 42 and cooling by means of the cooling water can be changed over. Straps 2 are formed on electrode plate leads 6, which are inserted within recesses 43, using a large metal mold 40, which is formed with recesses 43 of the shape of straps 2 which are to be formed.
This large metal mold 40 is heated by heaters 42 to 120.about.150.degree. C. and molten lead is poured into recesses 43, electrode plate leads 6 being inserted within recesses 43. At the point where the molten lead and the electrode plate leads 6 are welded, large metal mold 40 is changed over to cooling by cooling water. The molten lead that was poured in is thereby solidified, and on separating electrode plate group 10 from large metal mold 40, straps 2 are formed wherein the electrode plate leads 6 of electrode plate groups 10 are unitarily linked and joined.
Various proposals have been made in connection with the construction of this prior art example. In one of these (disclosed in Early Japanese Patent Publication No. H.6-290770 or Early Japanese Patent Publication No. H.8-255608), the aforesaid large metal mold 40 is reduced in size, within a range in which strap formation is possible, and the heating efficiency is raised by heating the mold by electromagnetic heating using an induction heating coil arranged at its periphery. In another of these (disclosed in Early Japanese Patent Publication No. H.5-3028), the metal mold is filled with a prescribed quantity of molten lead by immersing the metal mold in molten lead, and a step of cooling using air cooling is performed after insertion of the electrode plate leads therein, whilst the mold is circulated round a rotating table.
However, with the conventional method of manufacture using the cast-on strap system, when the electrode plate leads are inserted into the molten lead that has been poured into the metal mold, or when the molten lead is poured into the metal mold in which the electrode plate leads have been inserted, this produces an abrupt drop in the temperature of the molten lead and it is therefore necessary to raise the temperature of the molten lead in anticipation of this. As a result, lead oxide is liable to be produced, with the consequence that straps may be formed by molten lead containing impurity. Also, due to the sudden lowering of the temperature of the molten lead, welding with the electrode plate leads cannot be performed in a stable manner. Also, because the mold was large or because appropriate means for cooling when the molten lead was solidified were not adopted, the problems were experienced that straps were formed in which voids were produced or the cooling rate was slow, making it difficult to raise productivity.